Dissolution of Iron Oxides and Oxyhydroxides in Hydrochloric and Perchloric Acids

Abstract

Abstract--The dissolution of synthetic magnetite, maghemite, hematite, goethite, lepidocrocite, and akaganeite was faster in HCI than in HCIO4. In the presence of H § the C1-ion increased the dissolution rate, but the 004-ion had no effect, suggesting that the formation of Fe-Cl surface complexes assists dissolution. The effect of temperature on the initial dissolution rate can be described by the Arrhenius equation, with dissolution rates in the order: lepidocrocite > magnetite > akaganeite > maghemite > hematite > goethite. Activation energies and frequency factors for these minerals are 20.0, 19.0, 16.0, 20.3, 20.9, 22.5 kcal/ mole and 5.8 • 1011, 1.8 • 101~ 7.4 • 10 7, 5.1 • 101~ 2.1 • 101~ 3.0 x 1011 g Fe dissolved/mZ/hr, respectively. The complete dissolution of magnetite, maghemite, hematite, and goethite is well described by the cube-root law, whereas that of lepidocrocite is not.

A revised scheme for the reactivity of iron (oxyhydr)oxide minerals towards dissolved sulfide

“…Rate constants for the Fe (oxyhydr)oxide minerals range over 4 orders of magnitude when expressed in terms of (Fe 3+ ), and two orders of magnitude when expressed in terms of surface area. This wide range in reactivity is consistent with previous studies of the reductive and non reductive dissolution of Fe (oxyhydr)oxides (Sidhu et al, 1981;Postma, 1993), although actual dissolution kinetics vary considerably for different dissolution reactions.…”

“…The order of mineral reactivity determined when rate constants are expressed in terms of surface area (goethite < hematite < magnetite << lepidocrocite ≈ HFO; Table 2) is consistent with previous studies of both non-reductive dissolution (Cornell et al, 1974;Sidhu et al, 1981) and reductive dissolution by ligands other than sulfide (Postma, 1993).…”

Iron isotopic fractionation during continental weathering

“…However, it is possible that goethite and hematite in the sample were partially dissolved and contributed Fe to the sample [6]. In 0.5N HCl at 25˚C, goethite and hematite dissolve 10 to 100 times slower than less crystalline oxides such as lepidocrocite and akaganeite [7]. Hence the leaching procedure is unlikely to have dissolved more than a small fraction of the goethite and hematite while completely dissolving the less crystalline and amorphous components.…”

Preparo de nanocompósitos maghemita e polianilina assistido por ultrassom

“…Essa perda de massa é relacionada à solubilidade relativa das partículas em ácido clorídrico [23] , potencializada pelo efeito dispersivo altamente energético do ultrassom. Esses valores de perda foram usados para o cálculo dos efeitos da quantidade de maghemita e da potência de sonicação sobre a perda de maghemita.…”